The present invention relates generally to semiconductor fabrication methods and systems. The present invention also generally relates to chemical mechanical polishing (CMP) devices and techniques thereof. The present invention additionally relates to techniques and systems thereof for monitoring the quality of slurries utilized in CMP operations.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes successively more non-planar. This occurs because the distance between the outer surface and the underlying substrate is greatest in regions of the substrate where the least etching has occurred, and least in regions where the greatest etching has occurred. With a single patterned underlying layer, this non-planar surface comprises a series of peaks and valleys wherein the distance between the highest peak and the lowest valley may be the order of 7000 to 10,000 Angstroms. With multiple patterned underlying layers, the height difference between the peaks and valleys becomes even more severe, and can reach several microns.
This non-planar outer surface presents a problem for the integrated circuit manufacturer. If the outer surface is non-planar, then photolithographic techniques used to pattern photoresist layers might not be suitable, as a non-planar surface can prevent proper focusing of the photolithography apparatus. Therefore, there is a need to periodically planarize this substrate surface to provide a planar layer surface. Planarization, in effect, polishes away a non-planar, outer surface, whether conductive, semiconductive, or insulative, to form a relatively flat, smooth surface. Following planarization, additional layers may be deposited on the outer surface to form interconnect lines between features, or the outer surface may be etched to form vias to lower features.
Chemical mechanical polishing is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head, with the surface of the substrate to be polished exposed. The substrate is then placed against a rotating polishing pad. In addition, the carrier head may rotate to provide additional motion between the substrate and polishing surface. Further, a polishing slurry, including an abrasive and at least one chemically-reactive agent, may be spread on the polishing pad to provide an abrasive chemical solution at the interface between the pad and substrate.
Important factors in the chemical mechanical polishing process are: the finish (roughness) and flatness (lack of large scale topography) of the substrate surface, and the polishing rate. Inadequate flatness and finish can produce substrate defects. The polishing rate sets the time needed to polish a layer. Thus, it sets the maximum throughput of the polishing apparatus.
Each polishing pad provides a surface, which, in combination with the specific slurry mixture, can provide specific polishing characteristics. Thus, for any material being polished, the pad and slurry combination is theoretically capable of providing a specified finish and flatness on the polished surface. The pad and slurry combination can provide this finish and flatness in a specified polishing time. Additional factors, such as the relative speed between the substrate and pad, and the force pressing the substrate against the pad, affect the polishing rate, finish and flatness.
The mixing ratio of a slurry utilized in a chemical mechanical polishing operation is extremely sensitive in the performance of a slurry. Thus, it is important to be able to monitor the quality of a slurry, and hence, its associated mixing ratio, prior, during and after a polishing operation. This is particularly true with high selectivity slurries. The lack of in-situ slurry monitoring techniques usually results in unstable and inconsistence slurry polishing performances. The present inventors have thus concluded, based on the foregoing, that a need exists for a method and system for reliably monitoring the mixing-ratio of a slurry utilized in a chemical mechanical polishing operation.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention, and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is therefore one aspect of the present invention to provide an improved semiconductor fabrication method and system.
It is therefore another aspect of the present invention to provide an improved chemical mechanical polishing (CMP) method and system utilized in semiconductor fabrication operations.
It is still another aspect of the present invention to provide a method and system for in-situ monitoring of the quality of a slurry utilized in a chemical mechanical polishing (CMP) operation.
It is yet another aspect of the present invention to provide a method and system for in-situ monitoring of the mixing ratio of a slurry utilized in a chemical mechanical polishing operation.
The above and other aspects of the present invention can thus be achieved as is now described. A method and system for monitoring the quality of a slurry utilized in a chemical mechanical polishing operation is disclosed herein. A slurry is generally delivered through a tubular path during a chemical mechanical polishing operation. A laser light is generally transmitted from a laser light source, such that the laser light comes into contact with the slurry during the chemical mechanical polishing operation. The laser light can then be detected, after the laser light comes into contact with the slurry to thereby monitor the quality of the slurry utilized during the chemical mechanical polishing operation. The laser light that comes into contact with the slurry can be also be utilized to monitor a mixing ratio associated with the slurry. The laser light source may be integrated with a chemical mechanical polisher utilized during the chemical mechanical polishing operation. The laser light may comprise a fixed-wavelength laser light source.
The laser light may pass through an optical component after the last light comes into contact with the slurry. Thereafter, the laser light may be focused on a diffraction grating and thereby detected utilizing at least one spectrometer thereof. The tubular path through which the slurry flows may comprise a window located on a slurry line utilized in the chemical mechanical polishing operation. A rate of removal of the slurry may be predicted utilizing data associated with the laser light, after the laser light comes into contact with the slurry.
An alternative method and system for monitoring a mixing ratio of a mixture utilized in a chemical mechanical polishing operation is also disclosed herein. In such an alternative method and system, an abrasive component may be combined with an additive component to form a mixture thereof, wherein the mixture comprises a particular ultraviolet absorption spectra. The abrasive component and additive component may thereafter be diluted. Next, the particular ultraviolet absorption spectra may be analyzed such that the particular ultraviolet absorption spectra reflects a concentration of each component comprising the mixture, thereby providing data thereof indicative of the mixing ratio of the mixture utilized in the chemical mechanical polishing operation. A calibration curve can be established based on a known mixing ration mixture (e.g., 2:1, 1:1, 1:2, 1:3, etc). A concentration of each component (i.e., abrasive and additive) can be estimated from the calibration curve. The mixture generally comprises a slurry utilized in the chemical mechanical polishing operation. The abrasive component may be combined with the additive component in-line to form the mixture (i.e., slurry) thereof.